1. Field of the Invention
The present invention relates to a power transmission chain belt which connects two pulleys to transmit motion and power from one of the pulleys to the other.
2. Discussion of the Related Art
In recent years, substantial studies have been conducted to develop a belt-and-pulley type continuously variable transmission for a motor vehicle. This type of continuously variable transmission is provided with a pair of variable-diameter pulleys, each of which has a V-shaped circumferential groove whose width is variable to change an effective diameter of the pulley. These pulleys are connected by a transmission belt to transmit power therebetween. The speed ratio of the transmission is varied as the effective diameters of the pulleys are changed.
As a transmission belt used for the belt-and-pulley type continuously variable transmission of the type indicated above, there is known an endless chain belt which includes multiple sets of link plates connected in a loop by pins, each set consisting of a plurality of link plates which extend through an aperture formed in a block which is adapted to be in pressed contact with the pulleys. An example of such a chain belt is disclosed in laid-open Publication No. 40-13929 of examined Japanese Utility Model Application. This chain belt is shown in FIGS. 22-25, wherein the chain belt generally indicated at 3 consists of a plurality of link plates 4, 5, pins 6 and blocks 7. As depicted in FIG. 25, each link plate 4, 5 has pin holes 4a, 4a (5a, 5a) formed through its opposite end portions. The link plate 4, 5 has a pair of tabs 4c (5c) formed at one of the opposite end portions. Each tab 4c (5c) defines a shoulder 4b (5b). The pins 6 extend through the pin holes 4a, 5a of the link plates 4, 5 over a suitable distance such that the ends of the pins do not contact the opposed surfaces of the V-groove of the pulley. The pins 6 connect the individual link plates 4, 5, such that the link plates are pivotable about the pins. As indicated in FIG. 24, each block 7 has opposed angled surfaces 7a, 7a frictionally engageable with the opposed surfaces of the V-grooves of the pulley, and a central aperture 7b. The link plates 4 and 5 are inserted through the central aperture 7b of the appropriate block 7 in the opposite directions, alternately, such that the shoulders 4b, 5b of the tabs 4c, 5c of the link plates 4, 5 are held in abutting contact with front and rear surfaces 7F, 7R of the block 7, as depicted in FIG. 23. In this condition, the pins 6 are inserted through the pin holes 4a, 5a of the link plates 4, 5. Thus, the multiple sets of the link plates 4, 5 are connected into the endless chain belt 3, such that the pins 6 are held away from the front and rear surfaces 7F, 7R of the blocks 7, by the tabs 4c, 5c.
When the known chain belt of the type described above is installed in engagement with the circumferential grooves of the pulleys, the pins 6 are disposed along a part of each pulley such that the axes of the pins 6 define a part of a polygon. Consequently, the chain belt suffers from a variation in its tension, as indicated in FIG. 27. Described more specifically referring to FIG. 26, upon rotation of the input or drive pulley 1, a tension T1 of the slack side of the belt and a tension T2 of the tensile side vary as indicated in FIG. 27. Accordingly, a varying total amount of the tensile forces T1 and T2 of the belt is imparted to the shafts which support the pulleys. As a result, a support structure for supporting a transaxle case is oscillated, and the entire transaxle assembly is vibrated, causing noises to be heard within the interior of the vehicle.
If the length of each side of the polygon partially defined by the axes of the pins 6 disposed around the pulley is shortened, masses of the end portions of the link plates 4, 5 which define the pin holes 4a, 5a should be reduced to avoid an interference with the blocks 7, whereby the strength of the link plates 4, 5 is decreased. On the other hand, the chain belt tends to be large-sized if designed to provide a sufficient strength while using the link plates 4, 5 which have a relatively small distance between the pin holes 4a, 5a. This is undesirable for a continuously variable transmission for a motor vehicle, on which a space available for the chain belt is relatively limited. Due to the above inconveniences, it has been impossible to shorten the bending pitch of the chain belt (spacing between the adjacent pins 6) to an extent to sufficiently reduce the noises which occur due to the varying amount of tension of the chain belt of the transmission.